When the [artist id="968"]Beastie Boys[/artist]' Adam Yauch announced Monday that he had cancer and the Beasties would be canceling all upcoming tour dates and pushing back the release of their Hot Sauce Committee, Part One album, it came as a shock not just to fans, but to concert promoters too.

The Beastie Boys had been scheduled to headline four summer festivals — next weekend's All Points West in New Jersey; the Osheaga Fest (August 1-2 in Montreal); Lollapalooza (August 7-9 in Chicago); and the Outside Lands Festival (August 28-30 in San Francisco) — and the announcement left each event with a gaping hole to fill atop the bill.

So what does the Beasties' cancellation mean for each festival? Have promoters been inundated with refund requests from fans gearing up to see Yauch and company? And who will they secure to replace the band in the headlining slot?

MTV News attempted to contact representatives for each of the festivals but have yet to receive answers from any of them. A spokesperson for All Points West replied in an e-mail that they were "checking in" to our inquiry and would be in touch. E-mails and phone calls to the Gillett Entertainment Group — the Canadian promoters behind Osheaga — were not returned, but on Monday, the company issued a statement saying it is "exploring all options" for replacing the Beasties and urged fans to "please hold on to [their] tickets until further notice."

A spokesperson for Superfly Presents — which handles Outside Lands — did not respond to an e-mail, but like Osheaga, organizers for the festival posted a brief message online sending their thoughts to Yauch and his family and promising that updated information about the lineup would be forthcoming.

On Tuesday (July 21), C3 Presents, the Texas-based concert promoters behind Lollapalooza, announced that the Yeah Yeah Yeahs were stepping in to the Beasties' Saturday night slot. C3 partner Charlie Jones told the Chicago Tribune that the loss of the Beasties hadn't caused the festival to see an increase in refund requests: "People buy Lollapalooza tickets for the overall event, the overall experience. With the number of bands playing, the price is worth it."

The Beastie Boys had also been announced to headline the annual Austin City Limits festival in October, and while no replacement has been announced for them just yet, there are reports that the Kings of Leon — who were already announced as one of the fest's headliners — were going to pull double duty, playing a second headline slot in place of the Beasties. However, a spokesperson for ACL told MTV News that those reports were false: "We have not announced a replacement for the Beastie Boys yet."

In his message to fans, Yauch apologized "to anyone who's made plans or [was] psyched to come to these shows that are coming up," but promised that the Beastie Boys will "be back doing this soon." He also said he would begin treatment "probably next week."

A spokesperson for the Beasties told MTV News that he didn't know when Yauch's treatment would begin, and said that, for now, the group's upcoming Hot Sauce album is saddled with a "TBD" release date.